This invention relates to a cellulosic electrolytic capacitor spacer material loaded with a synthetic hydrotalcite and to an aluminum electrolytic capacitor utilizing it.
The single most prevalent failure mode for aluminum electrolytic capacitors is the accidental inclusion or entry of chloride ion into the capacitor. The chloride ion, primarily as sodium chloride, is ubiquitous in our environment inasmuch as it is present in our skin, in the food we eat, and even, in some locations, in the air. Capacitor fabrication and assembly involve hand operations and are carried out in the ambient atmosphere. Even with great care and extensive precautions it is difficult to prevent 100% the accidental entry of chloride ion into the capacitor.
Another source of chloride contamination is in the electrolyte used. Some materials used as solutes involve chloride in their commercial synthesis. Even repeated recrystallization does not remove all traces of chloride. Also, the electrolytes are chemically active materials and can extract chloride from rubber and plastic parts of the capacitors, particularly sealing means. The foil itself is a possible source of chloride contamination as the foil is etched using chloride reagents. Even though the foil is cleaned after etching, some chloride may remain trapped in the etch structure.
The presence of chloride ion in an aluminun electrolytic capacitor, even in the parts per million range, can seriously impair the functioning of the electrolyte system and also cause extensive corrosion of the aluminum electrodes. A means or mechanism for neutralizing the adverse effect of chloride that makes its way into an aluminum capacitor is eminently desirable.
Heretofore, materials have been added to the electrolyte system to react preferentially with chloride ion to prevent corrosion of the aluminum electrodes. Additives have been incorporated into rubbers and plastics to nullify or tie-up residual chlorides present in them. Some of the materials used in the past pose toxicity and disposal problems, e.g., nitro- and azo-compounds.